Conventionally, there has been proposed a vehicle seat that can transform states (postures) thereof as shown in FIGS. 12 to 14. The vehicle seat is provided with a seatback A pivotally attached to a floor panel B of a vehicle body, a seat bottom C pivotally attached to the seatback A, and a leg portion D pivotally attached to the seat bottom C.
The vehicle seat is transformed into any of three states: an ordinary state (FIG. 12), a tip-up state where the seat is totally upright (FIG. 13) and a dive-down state where the seat is stored in a recess portion E on the floor panel B (FIG. 14). Under the tip-up state or the dive-down state, the seatback A, the seat bottom C and the leg portion D are stacked in parallel to each other.
The vehicle seat has a lock mechanism that locks the seat bottom C to the seatback A when the seat bottom C is moved to a storage position in parallel to the seatback A. Accordingly, in order to return the seat bottom C to a horizontal use position under a state shown in FIG. 13, the lock mechanism needs to be unlocked. The lock mechanism operates even under a state shown in FIG. 14. Accordingly, to return a state shown in FIG. 14 to a state shown in FIG. 12, the lock mechanism needs to return to an unlock state.
A problem of the lock mechanism being placed into a lock state under a dive-down state has been solved by a vehicle seat proposed in JP2005-212554A. The vehicle seat is provided with a release function that makes the lock mechanism inoperable when the vehicle seat is placed into a dive-down state.    Patent Document 1: JP 2005-212554A1.